The present invention relates to the laser desorption of CVD precursor species and, more particularly, to the desorption of CVD precursor species by heating a target at a rate designed to selectively desorb relatively cool molecules therefrom. Further, the present invention relates to chemical vapor deposition incorporating the laser desorption technique of the present invention.
Stated broadly, chemical vapor deposition (CVD) includes any process in which a material is deposited on a substrate by decomposition of one or more precursor materials within a process chamber. In conventional CVD, the precursor is carried into the process chamber by a carrier gas flow by gradually heating the precursor to a temperature above its vaporization temperature such that the vaporized precursor is entrained in the carrier gas flow. Unfortunately, some CVD precursor materials are difficult to vaporize quickly and uniformly. Other CVD precursors are thermally unstable (i.e., the precursor decomposes) at temperatures required for sublimation. Additionally, the present inventor has identified specific CVD precursor materials characterized by respective decomposition and vaporization temperatures which are very nearly the same. Accordingly, it would not be practical to utilize conventional precursor heating schemes to introduce these precursors into a CVD carrier gas stream because significant decomposition of the precursor would occur upon heating.
Accordingly, there is a need for a system wherein CVD precursor species may be entrained in a carrier gas or otherwise transported to a CVD process without raising the temperature of the CVD precursor to its characteristic vaporization temperature.